1. Field of the Invention
The present invention relates to a device, a method and a corresponding computer program for the cylinder equalization of a lambda-controlled internal combustion engine, in particular of a motor vehicle.
2. Description of the Related Art
In a lambda-controlled internal combustion engine, for example, a gasoline engine including a three-way exhaust catalytic converter and a lambda sensor, the air-fuel ratio is regulated during homogeneous operation by the lambda control in such a way that the lambda mean value of the mixture composition for all cylinders has the value lambda=1.0 and thus ensures a low-emission operation.
Unequal distribution of the lambda values of individual cylinders takes place due to metering tolerances in the fuel metering of the internal combustion engine, which is carried out with the aid of injectors, for example, and due to cylinder-individual differences, which are caused by system tolerances, in the mixture composition, i.e., the cylinder charge with fuel and air, although the mean value for all cylinders assumes the desired lambda value 1.0. Thus, for example, in a four-cylinder engine, lambda (cylinder 1)=1.1, lambda (cylinder 2)=0.9, lambda (cylinder 3)=1.2, and lambda (cylinder 4)=0.8 may be provided, which corresponds as a whole to a mean value of lambda=1.0.
This imbalance between the individual cylinders results in an increase of the fuel consumption and an increase of exhaust gas emissions. The emission legislation which is applicable in many countries therefore prescribes exhaust gas diagnosis or regulating strategies which counteract or prevent this imbalance.
A generic method is known from Published German patent application document DE 195 27 218 A1, in which a possible unequal distribution of cylinder lambda values is derived from a detected uneven running of the internal combustion engine, i.e., the change of the engine torque after a sudden leaning. This is based on the technical effect that there is an unambiguous relationship between the mixture composition and a crankshaft acceleration resulting from the combustion. Cylinder-individual lambda differences of individual cylinders are adapted in that the cylinders are successively leaned and a cylinder-individual feature for trimming the respective cylinder is derived from the detected uneven running change. It is additionally ensured by the simultaneous enrichment of the non-leaned cylinders that the mean value of lambda remains constant at 1.0 for all cylinders.